BRPI0709067A2 - ventilatory control system - Google Patents

Abstract

VENTILATORY CONTROL SYSTEM. A system (50) is provided to deliver a flow of respiratory gas to a patient's airway. The system includes a pressurized flow module that generates a pressurized flow of respiratory gas and a patient circuit (56) coupled to the pressurized flow module configured to communicate the flow of respiratory gas to a patient's airway. The system includes a sensor (61, 62) to monitor a characteristic of a patient's breathing pattern, a controller that communicates with the sensor configured to increase a fraction of inspired carbon dioxide if the characteristic exceeds a higher threshold value and provides servo-ventilation if the characteristic is less than a lower threshold value. The upper threshold value and the lower threshold value are changed based on the monitored characteristic of the patient's breathing pattern.

Description

"VENTILATORY CONTROL SYSTEM"

PRIORITY CLAIM

Under the provisions of 35 U.S.C. § 119 (e), this patent application claims the benefit of U.S. Provisional Application no. 60 / 784,127, filed March 20, 2006.

TECHNICAL FIELD

The present invention relates to the treatment of various forms of sleep-disordered breathing, and more particularly to treating sleep-disordered breathing with an adaptive, state-dependent, positive airway pressure system.

BACKGROUND OF THE INVENTION

Sleep breathing disorder (SDB) is a common condition with important clinical consequences for affected individuals. Doctors and other experts have suggested that SDBexists as a continuous amount between a pure central apnea (caused by a lost breathing conduction) and a pure obstructive apnea (due to upper airway mechanics). Obstructive sleep apnea (OSA) is characterized by repetitive collapse of the upper airway during sleep as a result of lost compensation during sleep for an anatomical deficiency. This gives episodes of reduced air flow, hypoxemia (low blood oxygen level), hypercapnia (elevated circulating carbon dioxide, CO2), and sleep arousal to restore a stable airway. However, emerging data suggest that the pathophysiology of SDB is not limited only to upper airway collapse.

Breathing is the process where CO2-deficient, O2-rich air is brought into the lungs with contraction of the diaphragm and / or chest muscle so that CO2 in the deoxygenated CO2-rich blood returning to the lungs can passively follow its concentration gradient and diffuse. from blood to the alveoli and O2 can follow its concentration gradient from the alveoli to the blood. Breathing is regulated through negative feedback. The primary variable controlled by this system is CO2 in the bloodstream, measured as the carbon dioxide partial pressure, PCO2. An increase in PCO2 in the central and peripheral chemoreceptors leads to a compensatory increase in ventilation (ie, ventilation is used to release the body from CO2) and a decrease in PCO2 in the chemoreceptors leads to a decrease in ventilation. Thus, PCO2 is kept within a physiological range controlling ventilation. If the negative feedback from this system is compromised, then a given ventilatory disorder (eg increased ventilation with a sleep arousal), the resulting ventilatory response may be amplified rather than restrained. This can lead to episodes of hyperventilation followed by central apnea (a form of SDB that may have little to do with upper airway collapsibility).

The respiratory control system can be modeled as a system of compartments (brain compartment, pulmonary compartment, etc.) interconnected by the vasculature. Carbon dioxide flows through the bloodstream between these compartments. The plant compartment describes the input-output relationship between ventilation and oPCO2 in the lungs and consists of two sub-compartments, the lungs and body tissues. The plant can be described by a system of nonlinear first-order differential equations, but can be simplified using the concept of plant gain that represents the change in alveolar partial pressure of carbon dioxide PaCO2 over the ventilation (APAC02 / Aventilation). Under ambient air conditions, plant gain determines the decrease in PaCO2 (thereby increasing the gradient of CO2 concentration between blood and alveoli) for a given increase in ventilation. Thus, limiting the decrease in PaCO2 (i.e. decreasing the CO2 concentration gradient) with ventilation increasing the alveolar CO2 concentration decreases the plant compartment gain. Because the overall gain of ventilatory control is a product of all compartment mice, decreasing plant gain reduces the respiratory system instability of the entire system and helps curb the response to a given disorder.

Numerous studies have shown that positive airway pressure administered with a patient interface, such as a mask, can effectively treat OSA when titrated to the appropriate pressure, and in most cases will also improve sleep architecture. Data also suggest that there are significant clinical benefits to treating OSA. However, there is reason to believe that poor adherence to therapy (ie, continuous sleeping time spent on prescribed continuous positive airway pressure (CPAP) is less than the target) and significant residual SDB during therapy may have negative consequences with respect to clinical outcomes.

Cheyne-Strokes Respiration (CSR) is another form of sleep disordered breathing observed in some individuals with increased sensitivity to chemical respiratory stimuli. It is usually associated with cardiac arrest, but may also be a co-morbidity of some neurological conditions. FIG. 1 illustrates a typical Chey-ne-Strokes (CSR) breathing pattern 30 which is characterized by increasing periods 32 and rhythmic breathing periods 34, with periods of regular recurrence of high respiratory conduction (hyperpnea) 36 and conduction respiratory failure (hypopnea or apnea) 38. A typical Cheyne-Strokes cyclode, generally indicated at 40 in FIG. 1, lasts approximately one minute and is characterized by an increasing shape (arrow A) in which the patient's peak respiratory flow increases over several breath cycles, and decreasing variation (arrow B) in the peak flow where the patient's peak respiratory flow decreases in several cycles of breathing. Sleep fragmentation, as well as periodic arterial oxygen desaturation (PO2), forces the cardiovascular system and specifically the heart. Hyperpnea often causes arousal and thus degrades sleep quality. Emerging data suggest that an adaptive algorithm that can provide noninvasive mechanical ventilation when central apneas are detected and support ventilation when instantaneous peak airflow drops. below an adaptive threshold can significantly reduce or even eliminate CSR by increasing ventilation during a low respiratory conduction state.

Others have shown in independent studies that CSR can be significantly reduced and even eliminated in the laboratory with inhaled CO2 or mortaged space to promote CO2 re-inhalation (ie, interventions to reduce plant gain). FIG. 2, by Lorenzi-Filho G., Rankin F., Bies I., Bradley T. D .; Effects of Inhaled Carbon Dioxide and Oxygen of Cheyne-Stokes Respiration in Patients with Heart Failure, American Journal of Respieratory and Critical Care Medicine 1999; 159: 1490-1498, hereby incorporated by reference in its entirety, shows the elimination of CSR and central apnea by CO 2 inhalation (sample B) compared to air respiration (sample A). As shown in FIG. 2, several measurements were taken in the study to show the effects of CO2 and O2 dehumination including electroencephalogram (EEG), submental electromyogram (EMG) 1 tidal volume (VT), oxygen saturation (SaO2), tidalfinal carbon dioxide fraction (FetCO2) ) 1 and transcutaneous carbon dioxide (RcCO2) partial pressure.

It has also been successful to treat CSR in an intent-to-treat, low-flow outpatient CPAP-based experiment that promotes CO 2 re-inhalation. United States Patent No. 6,752,150 to Remmers et al. ("the Ί50 patent"), which is hereby incorporated by reference in its entirety, discloses a modified continuous positive airway pressure (CPAP) system designed to promote CO 2 re-inhalation to treat central apneas. In addition, the benefit of improving ventilatory control may be widespread beyond those with CRS or central apnea. Individuals with obstructive sleep apnea (OSA) who demonstrate emerging central CPAP apneas appear to have problems with upper airway collapsibility and ventilatory control. Thus, stabilizing the upper airway with positive airway pressure and decreasing plant gantry by increasing the alveolar CO2 concentration during episodes of hyperventilation may improve the effectiveness of positive pressure therapy in these individuals. In individuals with a stable upper airway, an intervention to decrease plant gain may be appropriate without the use of positive airway pressure.

United States Patent Application No. 10 / 716,360 (Publication No. US2004 / 0144383 A1) ("the '360 application"), which is hereby incorporated by reference in its entirety, discloses a system and method for treating respiratory disorder of the sleep providing accurate CO2 and O2 concentrations to the patient along with positive airway pressure.

An additional source of CO2 is supplied and mixed with a supply of O2 before being supplied to the patient. This configuration thus addresses the problems of sleep breathing disorders with respect to upper airway obstruction as well as abnormal breathing control (eg, CSR) as it maintains positive airway pressure flow.

Bi-level positive airway pressure therapy is a form of positive airway depression therapy that has advanced in the treatment of sleep apnea and other respiratory and cardiac disorders. In bi-level therapy, pressure is alternately applied to a patient's airway at relatively higher and lower pressure levels so that the therapeutic pressure is delivered alternately to a higher and lower magnitude force. Higher and lower magnitude positive prescriptive pressure levels are known as positive inspiratory airway pressure (IPAP) and positive expiratory airway pressure (EPAP), and are synchronized with the patient's inspiratory and expiratory cycle, respectively. .

An adaptive form of bi-level therapy, known as variable airway positive pressure (VarPAP), is disclosed in United States Patent No. 6,752,151 to Hill ("the Ί51 patent"), which is hereby incorporated by reference. in its entirety. The VarPAP system implements many of the standard functions of a positive airway pressure support device, as well as an algorithm that adjusts IPAP, EPAP, or both to counteract a CSR standard. A flow sensor is used to determine the patient's peak flow during breathing cycles, which allows a controller to monitor peak flows to determine if the patient is suffering from CSR or another sleep breathing disorder. The algorithm involves a three-layer process, each occurring at different time intervals to continually adapt the gaseous pressure provided to suit the patient's needs and detect any occurrence of sleep disturbance. In the case of a hypopnea or apnea period, known as central apneas as described above, VarPAP according to the disclosed system may provide a "machine breath" to stimulate breathing in the patient.

Another disclosure, US Pending Application No. 11 / 235,520 ("application '520"), which is hereby incorporated by reference in its entirety, is intended to improve the Ί51 patent and to make determinations based on instantaneous mean inspiratory flow and flow rate parameters. maximum mean respiratory rate. These average parameters serve to level or filter the direct instantaneous parameters used in the Ί51 patent and can therefore lead to higher results. Further improvements are made with respect to intra-breath flow monitoring and intensified disturbance detection.

DISCLOSURE OF INVENTION

According to one aspect of the present invention, a system is provided for releasing a flow of respiratory gas to a patient's airway. The system includes a pressurized flow module that generates a pressurized flow of respiratory gas and a patient circuit coupled to the pressurized flow module configured to communicate the respiratory flow to a patient's airway. The system includes a sensor to monitor a characteristic of a patient's breathing pattern, a controller that communicates with the sensor configured to increase a fraction of inspired carbon dioxide if the characteristic exceeds a higher threshold value, and to provide ifventilation is characteristic. is less than a lower threshold value. The upper threshold value and lower threshold value are changed based on the monitored characteristic of the patient's breathing pattern.

According to another aspect of the present invention, a system is provided to paralyze a respiratory gas flow to a patient airway and includes a pressurized flow module that generates a respiratory gas flow and a patient circuit coupled to the configured pressurized flow module. to communicate the flow of respiratory gas to a patient's airway. The system also includes a sensor for monitoring a characteristic of a patient breathing pattern and a carbon dioxide supplementation system associated with said patient circuit. A controller is operatively connected with the pressurized flow module and carbon dioxide supplement system. The controller communicates with the sensor and increases the amount of carbon dioxide patient circuit for patient inspiration if the feature exceeds a higher threshold value and controls the gas flow generator module to increase an inspiratory depression to expiratory pressure ratio provided to the patient's airway if the characteristic is less than a lower threshold value.

According to another aspect of the present invention, a method for determining the ventilation status of a patient undergoing respiratory therapy is provided. In the method, a flow of gas is released into the patient's airway from a source of respiratory gas through a patient circuit and a characteristic of a patient's breathing pattern is monitored. A lower threshold value is set for the characteristic based on an average characteristic value over a period of time and a higher threshold value is set for the characteristic by increasing or decreasing an initial value for the characteristic. The upper threshold value is decreased if a change in the mean characteristic value exceeds a predetermined limit, and the upper threshold value is increased by the frequency of a particular therapy provided to the patient exceeds a predetermined frequency.

According to another aspect of the present invention, a method is provided for treating a patient wherein a gas stream is released to the patient's airway from a respiratory gas source through a patient circuit and a characteristic of the patient's breathing pattern is monitored. A high breath state is predicted if a change in characteristic over a period of time is a positive value and exceeds a predetermined limit, and a low breath state is predicted if a characteristic change over a period of time is a negative value that has a value. absolute exceeding the predetermined limit. Appropriate treatment is applied to the combase patient in the predicted state.

According to another aspect of the present invention, a method of releasing pressurized breath gas to a patient's airway is provided. A gas flow is released to the patient's airway from a source of respiratory gas through a patient circuit and a characteristic of the patient's breathing pattern is monitored. An upper characteristic threshold value and a lower characteristic threshold value are determined based on the patient's breathing pattern and the inspired carbon dioxide fraction is increased if the characteristic value exceeds the upper threshold.

According to another aspect of the present invention, a method for determining an optimal therapeutic window in treating a patient is provided. An appropriate treatment dose is applied to the patient based on a predicted or existing state of respiration and a patient instability index in response to the applied dose is measured. A series of data points is recorded, representing the instability indices for each of a series of responses, and a therapeutic window is adjusted that corresponds to the dose applied with the instability index below the data points for which the measured index of instability. instability exceeds an acceptable value and above the data points for which the measured instability index is below an acceptable value.

According to another aspect of the present invention, a method is provided for treating a patient within an ideal therapeutic window wherein a dose of an appropriate treatment is applied to the patient based on a predicted or existing state of respiration. A patient instability index in response to the applied dose is measured and a series of data points representing the instability index for each of a series of responses is recorded. A therapeutic window is adjusted that corresponds to the dose applied with the instability index below the data points for which the measured instability index exceeds an acceptable value and above the data points for which the measured instability index is below an acceptable value. Subsequent doses of treatment within the therapeutic window are applied to the patient.

These and other objects, aspects, and features of the present invention, as well as the methods of operation and functions of related structure and coupling elements of parts and economies of manufacture, will become more apparent in consideration of the following description and the appended claims. with reference to the emanated drawings, these are all part of this descriptive report, wherein such reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. As used in the descriptive report and the claims, the singular form of "one", "one", and "the" includes plural referents unless the context of the contrary clearly dictates.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a typical Cheyne-Strokes breathing pattern including increasing periods and waning periods;

FIG. 2 shows the effect of increasing the fraction of inspired carbon dioxide in a Cheyne-Strokes breathing patient;

FIG. 3 is a schematic representation of an apparatus according to one embodiment of the present invention;

FIG. 4 is a schematic representation of a re-inhalation circuit according to one embodiment of the present invention;

FIG. 5 is a graphical representation of a normal breathing state according to one embodiment of the present invention;

FIG. 6 is a graphical representation of a low respiratory conduction state according to one embodiment of the present invention;

FIG. 7 is a graphical representation of a low respiratory conduction state according to another embodiment of the present invention;

FIG. 8 is a graphical representation of a high respiratory conduction state according to one embodiment of the present invention;

FIG. 9 is a schematic flow diagram of an algorithm for lowering a dynamic upper threshold according to an embodiment of the present invention;

FIG. 10 is a schematic flow diagram of an algorithm for increasing a dynamic upper threshold according to an embodiment of the present invention;

FIG. 11 is a graphical representation of a trend-based prediction method for predicting a high respiratory state when the respiratory measurement is peak flow in accordance with one embodiment of the present invention;

FIG. 12 is a graphical representation of a trend-based prediction method for predicting a high respiratory state when the respiratory measurement is volumetric, according to one embodiment of the present invention;

FIG. 13 is a graphical representation of a trend-based prediction method for predicting a low respiratory state when the respiratory measurement is peak flow in accordance with one embodiment of the present invention;

FIG. 14 is a graphical representation of a trend-based prediction method for predicting a low respiratory state when the respiratory measurement is volume according to one embodiment of the present invention; eFIG. 15 is a graphical representation of a statistical analysis method for determining an ideal therapeutic window according to one embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Individuals who demonstrate central sleep apnea, Cheyne-Strokes breathing, emerging central CPAP apneas, or other forms of breathing that indicate unstable breathing control appear to have elevated respiratory control instability describing the ventilatory response to a given ventilatory stimulus. The primary contributor to this increased respiratory control instability is probably an increased sensitivity to carbon dioxide (CO2) by central chemoreceptors (high controller gain). The present invention describes a method for counteracting this elevated respiratory control instability by decreasing ventilatory plant gain during a high respiratory conduction state and increasing ventilation during a low respiratory conduction state.

The functional elements of the apparatus used in the present invention may be similar to those disclosed in Ί51. As shown in FIG. 3, a state-dependent airway positive pressure support system 50 includes a gas flow generator52, such as a blower used in a conventional CPAP or bi-level device, or receiving breathing gas, generally indicated by arrow C from any suitable source, for example, a pressurized tank of oxygen or air from the ambient atmosphere, or a combination thereof. Gas flow generator 52 generates a respiratory gas flow, such as air, oxygen, or a mixture thereof, for release to a patient's airway54 at relatively higher and lower pressures, that is generally equal to or above ambient atmospheric pressure. Oxygen may be released to the patient to prevent oxyhemoglobin desaturation which may be the result of hypoventilation associated with a low respiratory conduction status and / or to stabilize respiratory control independent of the oxyhemoglobin saturation state.

Pressurized respiratory gas flow, generally indicated by arrow D of gas flow generator 52, is released via a release conduit 56 to a breathing mask or patient interface 58 of any known construction, which is typically used or otherwise attached to a patient 54 to communicate the respiratory gas flow with the patient's airway. Release conduit 56 and patient interface device 58 are collectively referred to as a patient circuit. An exhaust vent 57 indicated by arrow E may be included in patient interface 58, conduit 56, or any other suitable location. In one embodiment, exhaust port 57 may comprise an adjustable valve for altering the depression thrust in the patient circuit to increase or decrease trapped exhaled gas (and particularly CO2) for re-inhalation purposes. The valve may be manually adjustable or may be automatically controlled by a controller 64 via operative connection65 as discussed below. The apparatus according to the present invention may be a one or two member system as described in patente51, or may contain more than two members.

In one embodiment, some or all of the various conduit sections 56 may be provided by flexible tubing, rigid tubing, or other members that would provide a conduit for breathable gas to pass through them. Patient interface 58 is any application, invasive or noninvasive, such as a nasal mask, nasal / oral mask, full face mask, nasal cannula, endotracheal tube, or tracheal tube, suitable for communicating a provision of breathable gas into a patient's airway. The patient interface58 may include headgear for mounting the application to a patient's head. In addition, patient interface 58 may include controls mounted thereon to control at least one aspect of the patient care system. In the illustrated embodiment, patient interface 58 and / or conduit 56 includes (e) a suitable exhaust port 57 for exhausting gas from these components to the ambient atmosphere. Exhaust port 57 may be a passive exhaust port in the form of a continuously open port which imposes a flow restriction on the exhaust gas to permit control of gas pressure within the patient interface 58. Alternatively, exhaust port 57 may be an exhaust port. It assumes different settings to control the exhaust rate. Exhaust port 57 may communicate with controller 64 via operative connection 65 so that it is automatically and / or dynamically controlled by the system. Examples of suitable escape ports are taught, for example, in U.S. Patent Nos. 6,851,425 and 6,615,830, the contents thereof are incorporated herein by reference in this application.

In the embodiment illustrated, the state-dependent positive airway pressure support system includes a pressure controller in the form of a valve 60 provided at the release conduit 56. Valve 60 controls the flow gas pressure of the flow generator 52 released to the patient. For present purposes, flow generator 52 and valve 60 are collectively referred to as a pressurized flow module because they act in concert to control the pressure and / or gas flow released to the patient.

Referring to FIG. 3, the pressurized flow module including flow generator 52 and valve 60 is illustrated in accordance with one embodiment of the invention. In the embodiment shown in FIG. 3, pressurized flow module includes a flow generator 52 which receives breathable gas and raises the pressure of that gas for release to a patient's airway. Flow generator 52 is any device, such as a pump, blower, piston, or bellows that is capable of raising the pressure of the breathable gas received for release to a patient. As mentioned above, the present invention also contemplates that different atmospheric atmospheric air may be introduced into the system for patient release. In such embodiments, a pressurized gas-containing tube or tank containing air, oxygen, carbon dioxide, or another breathable gas mixture may provide flow to flow generator 52. In another embodiment of the pressurized flow module, The flow generator52 need not be supplied, but otherwise the breathable gas may be pressurized by the pressure of the pressurized gas tube or tank, with pressure released to the patient being controlled by a pressure regulator. In one embodiment, the flow generator 52 is a blower that is driven at a substantially constant speed during the course of the pressure support treatment to provide the gas in the system with a substantially high pressure and / or flow rate. constant.

In the embodiment of FIG. 3, the breathable gas is directed to the flow generator pressurized flow module 52 to a control valve 60. As described below, the control valve 60 and / or pressure generator 52 forms the pressurized flow module. which controls the circuit pressure and / or the gas circuit flow rate in the downstream circuit of the pressurized flow module. Examples of control valve 60 include at least one valve, such as a cuff or lift valve, that deflates the gas from circuit 12 as a method of controlling circuit pressure and circuit flow rate. US Patent No. 5,694,923 to Hete et al., The contents thereof are incorporated herein by reference, teaches a dual lift valve system suitable for use with control valve 60 which empties gas into the atmosphere and restricts gas flow. flow generator 52 to the patient.

For embodiments in which flow generator 52 is a blower operating at one speed only, then one or more control valve control settings 60 may be adjusted to provide control over circuit pressure and circuit flow rate for breathable gas. in the circuit. However, the present invention also contemplates modalities wherein one or more control settings related to the operation of flow generator 52, such as a blower speed, are adjusted alone or in combination with the control valves of control valve 60 to control the circuit pressure and the circuit flow rate rate for the breathable gas released to the patient. For example, a circuit pressure and a circuit flow rate near the desired circuit pressure and flow rate can be adjusted by adjusting an appropriate operating speed for flow generator 52 (macro control). Fine tuning (micro control) of circuit pressure and circuit flow rate can then be provided by adjusting one or more control adjustments associated with control valve 60 so that the two operating together determine the final circuit pressure to be downstream to the breathable gas in the pressurized flow module circuit.

It should be apparent that other techniques for controlling the pressure released to the patient by the pressurized flow module, such as varying the blower speed, either alone or in combination with a pressure control valve 60, are contemplated by the present invention. Thus, valve 60 is optional depending on the technique used to control the pressure of the respiratory gas flow released to the patient. If valve 60 is eliminated, the pressurized flow module corresponds to flow generator 52 alone, and gas pressure in the patient circuit is controlled, for example, by controlling the motor speed of flow generator 52. Another technique for Pressure control is to bleed the flow into the atmosphere, or into another member of the circuit using active or passively controlled valves.

State-dependent airway positive pressure support system 50 also includes a flow sensor 62 which measures the respiratory gas flow within the deliberate conduit 56. Flow sensor 62 is any suitable device for measuring these parameters, such as a spirometer, pneumotometer, variable orifice transducer, differential depression transducer, or other conventional flow transducer. According to a presently preferred embodiment shown in FIG. 3, flow sensor 62 is natubulated with release conduit 56, most preferably downstream of valve 60. Flow sensor 62 generates a flow signal that is supplied to a controller 64 and is used to determine the gas flow in the patient.

Of course, other techniques for measuring patient respiratory flow are contemplated by the present invention, such as measuring flow directly to the patient or at other locations along the release conduit 54, measuring patient flow based on operation. of the pressure generator, and measuring patient flow using a flow sensor upstream of the pressure generator. For example, U.S. Patent No. 6,017,315 to Starr et al., The contents thereof are incorporated herein by reference, teaches a quantitative flow member located at the patient interface. Flow can also be derived from other indirect parameters measured in the system, such as pressure, temperature, CO2 concentration, etc.

Another sensor block 61 is provided in the circuit shown in FIG. 3. The desensor block 61 may represent one or more additional sensors that may detect CO2, O2 (main flow or side flow), or some other appropriate measure to gather information regarding the properties of the gas being released or exhaled by the patient. The various sensors need not be located at the same location along the release apparatus, otherwise sensor block 61 is merely representative of the sensors that may be distributed throughout the apparatus. As such, CO2 measurements may be implemented at the patient interface 58, conduit 56, or anywhere else in the conduction and are not intended to be limited within the pressure supply circuitry50; they can be in the patient circuit as well. Measurements can be used and algorithms to determine the amount of CO2 in a reservoir or dead space. Measurements can be further used to determine how much CO2 retention or washing has occurred that can predict the principle of clinically undesired respiratory conduction states. This information can be used to drive decision making. Sensors can calculate scrubbing or stored CO2 by integrating measured CO2 levels flowing beyond a sensor multiplied over time by the flow during inhalation or exhalation. Measurements can be taken directly or indirectly.

The system may additionally include a humidifier 63. Although shown to be located on the patient circuit in FIG. 3, it will be understood that the humidifier 63 may be located elsewhere in the gas supply system, such as the positive airway circuit 50. The humidifier 63 also improves comfort by providing moisture in the gas provided. The humidifier can be configured to not only increase humidification but also to take moisture out of conduit 56 due to re-inhalation of exhaled moist air. Thus, the humidifier 63 may be a cold or heated humidifier or a humidity-controlling subsystem (by adding or removing moisture).

U.S. Patent Application No. 11 / 234,351, incorporated herein by reference in its entirety, discloses a humidifier device suitable for use in the present invention.

In addition, the pending provisional patent application U.S. 60 / 697,130, incorporated herein by reference in its entirety, discloses such a humidifying device for controlling the level of moisture within a fan circuit.

An input / output device 66 is provided for adjusting various parameters used by the state-dependent airway positive pressure support system, as well as for displaying and producing information and data for a user, such as a clinician or professional. Cheers. It will be understood that the present invention contemplates providing inlet / outlet terminals so that the operating information and data collected by the state-dependent airway positive pressure support system can be remotely monitored and controlled. Input / output device 66 may be any device suitable for providing information and / or commands to the controller 64 via an operative connection and presenting information to the patient, or other user, in a man-friendly format. . Examples of a suitable input / output device include an add-on keyboard, keyboard, touch pad, mouse, visual display (for example, LCD or LED screen), microphone, speaker, switches, knob, dial, lamps, or any other device. allow a user to enter information and receive information from the ventilation system.

Controller 64 is preferably a microprocessor that is capable of implementing and performing routines to monitor patient breathing characteristics and control respiratory gas flow based as discussed below in detail. Controller 64 is operably connected to the pressurized flow module (flow generator 52 and valve 60). For example, in the embodiment of FIG. 3, the output of sensors 61 and 62 may be provided to controller 64 comprising a processor for determining the instantaneous volume (V) of gas delivered to the patient, or the instantaneous flow rate (V ') of such gas to the patient, or both. For example, the instantaneous volume may be determined by integrating the measured flow rate of sensor 62. In embodiments where flow sensor 62 is relatively located away from patient interface 58 to determine the patient's current gas flow rate or flow rate. The patient's gas actuation flow, which is considered a negative flow controller 64 receives the output of sensor 62 as an estimated flow. Controller 64 processes this estimated flow information, for example by performing leak estimation, to determine the current flow in the patient's airway, as is known to those skilled in the art.

An example of a suitable re-inhalation circuit 46 for containing exhaled CO2 and releasing to the patient is described in FIG. 4. The inhalation circuit 46 may be integrated with the circuit shown in FIG. 3. Inhalation circuit 46 receives pressurized gas from pressure source 41 which may be the pressurized flow module as described and includes a flow meter 42. Rehalation circuit 46 includes a 3-port 2-position valve 43 which may be controlled by controller 64 or potentially the CPAP or bi-level device itself (ie, controlled by gas flow). Valve 43 may be in one of two states. During inhalation (Position 1; shown on the left side of FIG. 4), valve 43 is in a first position and circuit 46 is very similar to a traditional CPAP or bi-level pressure support system. However, there is a flow meter 42 in series with circuit 46 and the flow meter 42 may provide a real time value for the air flow or inspired volume (integrating the amount of air flow). During exhalation (E / R Position; shown on the right side of FIG. 4), valve 43 moves to the second position where exhaled air is directed to a tube-like circuit having a reservoir 44 for collecting exhaled gas, for example. , 500 ml. During inhalation, the inhaled volume or flow should exceed a preset level, valve 43 will be moved to the E / R position, thereby modifying the contained exhaled air and releasing it to the patient. Trigger signals can be provided by suitable algorithms for initiation of exhalation and inhalation. Additionally, an algorithm could be implemented that could determine a baseline inspired volume threshold, thereby eliminating the need for a predetermined or predetermined unspecified volume. Such an algorithm can be configured to adapt to the needs of the patient.

Three states of respiration are defined by the present invention and are delineated by two dynamic and adaptive quantitative limits: an upper threshold and a lower threshold. Upper and lower threshold values may refer to a suitable characteristic that indicates respiratory conduction, such as airflow. peak air, a medium peak flow, volumetidal, etc. When the indicative characteristic of a patient is between upper and lower thresholds, the patient may be considered to be renewing air normally.

When the indicative characteristic of a patient exceeds the upper threshold value, it is considered that the patient is in a state of high respiratory conduction. When the indicative feature of a patient falls below the lower threshold value, the patient is considered to be in a low state of respiratory conduction. A low state of respiratory conduction may be indicative of central apnea, hypoventilation, or another sleep-breathing disorder. High respiratory conduction periods followed by low respiratory conduction may be indicative of CSR. The dependent airway positive pressure system of the present invention applies varied interventions or therapies to a patient depending on the patient's particular respiratory state, and also applicable interventions or therapies at adaptive intensity levels depending on the patient. severity of the condition (ie, how far the patient's breathing is from the ideal).

It should be understood by those having skill in the art that, since threshold values are dynamic, they may under certain conditions converge to shrink the normal breathing window or eliminate it altogether. In the event that the normal breathing window becomes too small or nonexistent, the state-dependent positive airway pressure system of the present invention continuously varies the appropriate intervention effectively (e.g., increased doses of CO2 or O2, or adaptive servo-ventilation, as also discussed below) in proportion to the deviation of a target (ie, in proportion to the severity of respiratory status as determined by the deviation of fused thresholds). Present disclosure primarily refers to the system as identifying three distinct states, but it is appreciated that in all cases the thresholds may converge and result in a system that effectively applies appropriate intervention at an appropriate intensity based on the deviation of a given state. characteristic indicative of a simple value.

During the normal state of ventilation, which is when the patient's indicative characteristic is between the upper and lower thresholds, positive pressure therapy is released and determined by prescribed CPAP or bi-level adjustments during a sleep study or by an automated algorithm. to eliminate evidence of upper airway obstruction. The normal state of ventilation is shown in FIG. 5 depicting the patient's air flow over time. One skilled in the art would recognize that tidal volume or another feature may alternatively be used in the present invention as an indicator. An upper peak flow threshold 12 and a lower peak flow threshold 14 are determined (as discussed below) and, in the normal state as shown, the current air flow 10 of the patient peaks between the two thresholds.

As shown in FIG. 5, bi-level therapy including positive inspiratory airway pressure 16 (IPAP) and positive expiratory airway pressure 18 (EPAP) 1 remain constant during the normal state. In a device using CPAP therapy (not shown) instead of bi-level therapy, the level of continuous pressure released to the patient is equally constant. Known methods of expiratory pressure relief such as those provided by a C-Flex or Bi-Felx1 device that reduces expiratory pressure at the beginning of expiratory respiration may also be incorporated to improve patient comfort. A Bi-Flex device also controls inspiratory pressure based on the gas flow monitored by the system.

If the patient were to suffer central apnea 22, as shown in FIG. 6, there would be no detectable patient airflow 10 and the peak airflow of this modulator will fall below the lower threshold 14. Controller 64 receives flow information from flow sensor 62 and / or other sensors 61, comparing it with parameters threshold and makes the determination that the patient is in a low state of respiratory conduction. Determination can be done after a fixed period of time when no respiratory activity is detected or can be done adaptively based on historical breathing patterns.

In the low state, therapy delivered by the state-dependent positive airway pressure system shifts from minimal CPAP therapy or bi-level therapy as applied during the normal state. It should be noted that the terms CPAP or bi-level therapy are used for descriptive purposes, but other therapeutic modes or methods intended to treat apnea with an obstructive component are contemplated in the invention, such as proportional assisted ventilation (VAP) attempting to release of a flow based on the patient's breathing effort. In addition to prescribed CPAP or bi-level therapy, the state-dependent positive airway pressure system may release servoventilation, or variable airway positive pressure (VarPAP) to generate a patient breath. An adaptive system for providing positive variable airway pressure to a patient based on the recent history of the breathing pattern is disclosed in Ί51 and is incorporated herein by reference in its entirety. A positive variable airway pressure system using average time parameters is disclosed in the '520e patent application is also incorporated herein by reference in its entirety.

At patient ventilation, controller 64, communicating with flow generator 52 and / or control valve 60, increases the pressure ratio from IPAP to EPAP so that the positive airway pressure system helps maintain spontaneous breathing. by the patient (ie the patient renews the air on their own; known as "synchronous modes") or, in cases of central apnea where there is no patient spontaneous breathing, provides a "machine breath" to trigger spontaneous breathing. -Nea. Providing a series of machine breaths according to time-controlled intervals independent of patient activity is referred to as "time mode" and is also considered to be a servo-ventilation element. In "combination mode", ventilation is provided to assist the patient in breathing during spontaneous breathing as in synchronous mode and to provide machine breaths or synchronized breath control when the patient requires such control. As the severity of the condition decreases, the pressure ratio of IPAP to EPAP may be decreased accordingly. As is known in the art, changing the change in pressure between IPAP and EPAP can be accomplished by increasing / decreasing IPAP, decreasing / increasing EPAP1 or both. For example, to increase the ratio of IPAP to EPAP1, IPAP may be increased, EPAP may be decreased, or both may be performed. The change may be effected over a full breath or variously within a breath according to a predetermined or adaptive waveform.

As shown in FIG. 6, a central apnea 22 is detected after a period of time (which may be a preprogrammed or adaptably determined period) and a response 17 is elicited to it. In the scenario described in FIG. 6, response 17 is an increase in positive inspiratory airway pressure (IPAP), or a "machine breath", which is intended to stimulate spontaneous breathing by the patient. Subsequent machine breaths may be released to the patient at intensity levels and time intervals determined as required based on the patient's history and / or current condition.

In the low state of respiratory conduction, it may further be desirable to boost alveolar CO2 (PCO2) or the inspired CO2 fraction (FiCO2) to increase ventilation. Several methods are known in the art for effecting CO2 enhancement including controlling re-inhalation through an active leak valve, dynamically increasing dead space, providing an exhaled CO2 reservoir, or providing an additional source of CO2. The Ί50 patent, hereby incorporated by reference, discloses some of these mechanisms including an active leakage valve, dynamic dead space, an exhaled CO2 reservoir and an adjustable mask exhaust valve, and is hereby incorporated by reference in its entirety. '360 patent application discloses an additional source of CO2 which is mixed with O2 and is incorporated by reference in its entirety as well. Other methods of creating higher levels of CO2 that are present in the atmosphere are contemplated such as chemical generation, cryogenic cooling, molecular adsorption, and filtration of the patient's atmospheric gas or exhaled gas.

FIG. 7 shows the detection of a low state of respiratory conduction similar to that shown in FIG. 6 except that a small amount of ventilation is detected. In this case, peak breath airflow 13 falls below the lower threshold value14 and controller 64, thus declaring a low breathing state. As described above, controller 64 provides additional servo-ventilation therapy (VarPAP) to boost the patient's respiratory conduction. As shown in FIG. 7, IPAP 16 may be appropriately increased 17 during spontaneous breathing, as described in Ί51, in response to detected hypopnea. Methods for boosting FiCO2 or alveolar CO2 may also be implemented as described above (ie dynamic dead space, CO2 reservoir, active leak valve, etc.) to boost the patient's respiratory conduction as indicated by increases. 21 on the FiCO2 control 20.

If as shown in FIG. 8, patient indication characteristics 10 exceed the upper threshold 12, controller 64 determines that the patient is in a high respiratory conduction state. As shown in FIG. 8, peak flow exceeds the upper threshold 12 for peak flow at peaks 15. During this state, plant gain reduction therapy is implemented which involves holding the final tidal CO2 by increasing FiCO2 using a method described above, such as as maintaining dynamic dead space, using a captured CO2 reservoir or otherwise implementing re-inhalation. By maintaining adequate alveolar CO2, central apnea or hypopnea that often follows periods of hyperpnea can be attenuated (see characteristic apneas 38 following hyperpneas 36 in a typical CSR cycle as in Figure 1).

Although EPAP 18 is shown in FIG. As remaining constant during the high state of ventilation, the present invention also contemplates reducing EPAP 18 during exhaled breathing to improve the circuit's ability to recapture exhaled CO2 in certain re-inhalation techniques described above. EPAP 18 may be reduced by a predetermined constant level, according to a predetermined or adaptable waveform, impulsively based on patient history, impulsively, or by any combination of the preceding.

Another example of an apparatus for increasing re-inhalation with respect to FIG. 3, actively controlling the exhaust valve 57 so that the exhaled gas flows back to the conduit 56. The controller 64 may be operably connected via port 65 to control the degree of opening of valve 57 to prevent gas leakage. exhaled, thereby increasing the fraction of CO2 inspired by subsequent breaths. Another embodiment may use a CO2 reservoir (not shown) connected to the system near the patient interface 58 to capture exhaled gas and reinsert the gas into the patient airway. The reservoir can communicate with patient interface 58 or conduit 56 via a valve that can be actively controlled by controller 64.

Having thus described the three respiratory states and the interventions and therapies implemented in each, the disclosure will now turn to the determination of upper and lower threshold values and the establishment of a normal dynamic breathing window, i.e. the range between the upper and lower threshold values. It should be understood that the system according to the present invention may be implemented to provide self-titration therapy during any or all respiratory states. Self-titration refers to a minimum level of positive airway pressure provided to maintain a patient's upper airway. to prevent obstruction-related occurrences such as obstructive sleep apnea, snoring, hypopnea, etc.

To determine a dynamic upper threshold (DUT) 1 the system is initially set to a preset or initial value. A default value may be based on the patient's previous history or may be selected by the clinician. Alternatively, an initial value may be obtained based on a measured parameter, eg picomedial air flow over a period of time or average tidal volume over time. Two separate algorithms operated in parallel to determine the algorithm of a DUT acts to decrease DUT and other actions to increase DUT. Each will be dealt with in turn.

The DUT will be decreased if the system is not responding to unstable breathing. This algorithm calculates a change (eg, slope of an adjusted line) in the mean of a respiratory measure or indicative characteristic (eg, peak flow, volumetide, etc.). and, if the change exceeds a predetermined value, the DUT decreases by a quantity proportional to that change. If respiration is stable, then there will be little or no change in mean respiratory measurement over time, so no change is required for DUT. If respiration is unstable, then there will be changes over time in mean respiratory measurements, indicating a need for decreased DUT to make the system more sensitive in detecting a high respiratory conduction state.

With reference to FIG. 9, the algorithm for decreasing the DUT is schematically illustrated. In step 100, an average respiratory measurement, such as peak flow, tidal volume, or other measurement, is over a given time period, K1. In step 102, the change in mean respiratory measurement is over a period of time to obtain mRNA. At step 104, the controller determines whether the absolute value of ARm (| ARm |) is greater than a predetermined threshold value (T1) that can be preprogrammed by a full user such as a clinician.

If the absolute value of the change in respiratory measure | ARm | exceeds the boundary value T1, then the controller decreases the DUT in step 106 by an amount proportional to | ARm |. The value "c" in step 106 is a decreasing factor and can be programmed by a user. The c value can be such that the DUT can be incrementally decreased without adverse or abrupt effects on the patient.

Se | ARm | do not exceed the T1 threshold value, then no changes are made to the DUT as indicated in step 108. This result indicates that the patient's breathing pattern is constant and therefore system sensitivity need not be increased. to FIG. 10, there is schematically shown an algorithm for increasing the DUT. In determining whether the DUT should be increased, the question is essentially whether the system is very sensitive. Consequently, the number of breaths supported by CO2 gives a measure of system sensitivity and is therefore the measure used to determine if the DUT should be increased.

In step 200, the percentage of CO2-supported breaths re-inhalation is determined to obtain CO2Sup- This percentage is then compared to a preprogrammed threshold value T2 in step 202. If the percentage of CO2CO2Supp-supported breaths exceeds the threshold value T2, then the DUT is increased by an amount proportional to the percentage as indicated in step 204. The increase factor c may be pre-programmed by a user and may or may not be the same as the decrease factor used in the algorithm to decrease. the DUT, described above.

If the percentage of breaths supported by CO2 CO2Supp is lower than threshold value T2, then no change is made to the DUT as indicated in step 206. Result indicates that the system is not overactive in driving state intervention. high piracy rate and, consequently, the DUT need not be increased.

The determination of the dynamic lower threshold (DLT) is made in a manner similar to that used in the '51 patent and the '520 patent application, both of these methods are incorporated by reference. Briefly, an average respiratory measure or indicative characteristic (eg peak air flow, tidal volume, etc.) is obtained over a moving time period, such as two minutes, five minutes, or some other time period, and the DLT is dynamically fixed, or adjusted, to a predetermined factor below the moving medium. Thus, when the instantaneous respiratory measurement falls below the mean or adjusted moving average, controller 64 recognizes a low respiratory conduction state and initiates the corresponding intervention (s). Of course, there is no need for separate algorithms to increase and decrease DLT as the median measurement over time will inherently increase and decrease.

According to another aspect of the present invention, the state-dependent airway positive pressure system monitors a patient's breathing pattern and identifies trends or changes that predict unstable or clinically undesirable respiratory conduction states. If a change in respiratory conduction status is predicted, the system may activate or suspend appropriate therapeutic intervention (eg servo ventilation, increasing alveolar CO2, etc.) to prevent the state from being achieved. This represents an advantageous feature in which the system anticipates an undesirable state and acts to cure the condition before the undesirable state occurs. The system is adaptable in that it "learns" an appropriate therapeutic window based on the effectiveness of the actual therapeutic interventions performed on the patient. This system may be used in conjunction with a purely state-dependent system as described above or as an isolated system.

FIG. 11 shows the prediction of a high respiratory state based on an increasing peak flow trend. As shown, the first three peaks of flow 10 are within the normal respiratory window (ie, peaks are lower than upper threshold 12 and higher than lower threshold 14) but are tending to exceed upper threshold 12. The process by which trends are predicted and states of change are anticipated, the slope of respiratory measurement (here, peak flow) is first determined. If the slope24 exceeds a predetermined upper limit, then controller 64 activates or suspends appropriate intervention at point 26, such as CO2 re-inhalation or dynamic dead space, as discussed above with respect to current state changes. With this premature intervention, the predicted change in respiratory status can be reduced or prevented. Point 28 represents the point at which the system would have activated (or suspended) an intervention therapy without the use of trend prediction. Thus, prognosis arrest normalizes a patient's breathing pattern earlier than rigidly dependent on state and without having to wait for an undesirable state of ventilation to occur.

FIG. 12 shows a high respiratory conduction tendency, similar to FIG. 11, except that the respiratory measure 10 in this case is tidal volume. As before, the trend is predicted after three breathing cycles and the slope 24 is determined to exceed a predetermined limit. Intervention therapy is activated or discontinued, as appropriate, at point 26 before a current state change occurs and the undesirable effects of a state change are reduced or eliminated altogether.

FIGS. 13 and 14 show the prediction of a low respiratory state when the respiratory measure is peak flow and tidal volume, respectively. The trend is prognostic, similar to the prediction of a high respiratory state, based on the slope 24 of three successive respiratory cycles. If the slope exceeds a predetermined limit, then appropriate intervention therapy is activated or suspended accordingly. One skilled in the art would appreciate that several breathing cycles other than three can be used to predict trends as appropriate.

The system according to the present invention may also be made to be adaptable to a patient's present condition and determine an optimal therapeutic window. A therapeutic window refers to the effective range of a CO2 or O2 "dose" during an intervention. to stabilize breathing. FIG. 15 shows a graph of various samples taken from a patient that can be used by the system to determine the optimal therapeutic window. The vertical geometry axis measures the CO2 dose delivered to hold CO2 during high respiratory conduction. The CO2 dose can also be determined by the dead space volume. The instability index, measured along the horizontal geometrical axis, is a measure of the severity or proportion of unstable respiration due to changes in respiratory conduction, and may be derived from parameters such as a) a minimum and maximum ratio of such a measurement. such as peak flow or tidal volume, b) the slope of a line adjusted to an average (or median) window of motion such as peak flow or tidal volume, or c) a system loop measurement or predictor of gain respiratory control.

Therapeutic window 308 in FIG. 15 represents an appropriate range of CO 2 inspired dose or dead space volume used in a particular therapy. Data point 300 represents an occurrence of an unstable event while data point 302 represents an occurrence of a stable event. Stable event 302 is judged to be in an acceptable therapeutic window 308 based on the measured instability parameter (s). Doses of CO2 304 above the therapeutic window 308 cause hyperventilation and doses 306 below the therapeutic window 308 are not sufficient to stabilize respiration. In this way, by storing multiple data samples each day and deleting old data, the system can always be tuned to a patient's current condition and can be adjusted and adjusted to the therapy line based on instabilities. patient measures. That is, when a dose used in an intervention causes instability as determined by one or more of the measured instability parameters mentioned above, the controller associates that dose with or above or below the therapeutic window 308 and makes modifications to the therapeutic window 308 accordingly.

Because the above method is adaptable, it learns what is effective for individual patients. Adaptive systems require initial conditions that are programmed into the system and updated as patient therapy experience is gained. The system may be made more robust by using one or more of the many adaptive control techniques and statistics that are well described in the literature to make the system effectively patient-friendly, remote manipulated and / or poor data, etc.

Although this example describes an intervention for prognostic or existing hyperventilation, a similar picture and statistical analysis may be used for hypovertilation or central apnea. In which case, a graph can be plotted where CO2 and / or servo ventilation is / are used to treat the predicted or existing condition. Too much CO2 code in this case may cause additional CO2 flushing of the patient, exacerbating the central apnea. Too much CO2 could trigger hyperventilation.

Additionally, the system may require more than one dimension of therapy optimization data analysis, such as time data, on the number of physiological parameters introduced to the algorithm. For example, there may be hysteresis in the system, so the sequence of respiratory states leading to the present state would need to be known to apply the correct therapy.

Although the invention has been described in detail for the purpose of illustration on the basis that it is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is for that purpose only and that the invention is not limited to the disclosed embodiments. but, on the contrary, it is intended to encompass the equivalent modifications and arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, as far as possible, one or more features of any embodiment may be combined with one or more features of any other embodiment.

Claims (24)

1. System (50) for releasing a respiratory gas flow to a patient's airway, characterized by the fact that it comprises: a pressurized flow module that generates a pressurized respiratory gas flow; a patient circuit. (56) coupled to the pressurized flow module configured to communicate respiratory gas flow with a patient's airway, a sensor (61, 62) adapted to monitor a characteristic of a patient's breathing pattern; The controller (64) communicating with the sensor is configured to increase an inspired carbon dioxide fraction if the characteristic exceeds a higher threshold value and provides servo ventilation if the characteristic is less than a lower threshold value, where the threshold value The upper and lower threshold values change based on the monitored characteristic of the patient's breathing pattern. System according to claim 1, characterized in that the controller is configured to increase the fraction of inspired carbon dioxide in addition to providing servo-ventilation when the characteristic is less than the lower threshold value. System according to claim 1, characterized in that the controller is configured to increase the inspired carbon dioxide fraction (a) by re-inhaling, (b) providing an additional source of carbon dioxide, (c) providing carbon dioxide from a reservoir adapted to capture exhaust gas, (d) any combination of (a) - (c). System according to claim 1, characterized in that the pressurized flow module comprises a blower (52), a valve (60), or both. System according to claim 1, characterized in that the upper threshold value and lower threshold value are the same simple value. System according to claim 1, characterized in that the characteristic is patient peak flow or patient tidal volume. System according to Claim 1, characterized in that the controller provides servo ventilation providing an increasing ratio of inspiratory pressure to expiratory pressure. 8. System (10) for releasing a respiratory gas flow to a patient's airway, characterized by the fact that it comprises: a pressurized flow module that generates a respiratory gas flow; a patient circuit (56) coupled to the pressurized flow module configured to communicate respiratory gas flow to a patient's airway; a sensor (61, 62) to monitor a characteristic of a patient's breathing pattern; a carbon dioxide supplementation system (46) associated with said depacient circuit; and a controller (64) operatively connected with said pressurized flow module and carbon dioxide supplementation system, said controller communicating with the sensor and increasing an amount of carbon dioxide in said patient circuit for inspiration by if the feature exceeds a higher threshold value, the controller controlling said gas flow generator module to increase an inspiratory pressure to expiratory pressure ratio delivered to the patient's airway if the feature is less than a lower threshold value . System according to Claim 8, characterized in that the pressurized flow module comprises a blower (52), a valve (60), or both. A system according to claim 8, characterized in that the carbon dioxide supplementation system comprises: (a) a valve (43) which directs expired carbon dioxide back to the patient for re-inhalation; an external carbon dioxide source that communicates with the patient circuit, (c) a carbon dioxide reservoir (44) to capture exhaust gas, or (d) any combination of (a) - (ç). System according to claim 8, characterized in that the upper threshold value and lower threshold value are the same simple value. System according to claim 8, characterized in that the characteristic is patient peak flow or patient tidal volume. System according to Claim 8, characterized in that the system provides an increasing ratio of inspiratory pressure to expiratory pressure with a decrease in characteristic below the lower threshold value. 14. A method for determining ventilatory status of a patient undergoing respiratory therapy, characterized in that it comprises: releasing a patient's airway gas flow from a respiratory gas source via a patient circuit (56); a patient's breathing pattern, establish a lower threshold value over a period of time for the characteristic based on an average characteristic value; and establishing a higher threshold value for the characteristic by increasing or decreasing an initial value for the characteristic, the upper threshold value being decreased if a change in the mean value of the characteristic exceeds a predetermined limit, and the upper threshold value being increased if a frequency. of a particular therapy provided for the patient to exceed a predetermined frequency. A method according to claim 14, characterized in that the particular therapy provided to the patient is carbon dioxide re-inhalation. A method according to claim 14, characterized in that the lower threshold value is obtained by reducing the mean value over time by a predetermined factor. A method of treating a patient, characterized by the fact that it comprises: releasing a patient's airway gas flow from a respiratory gas source through a patient circuit, monitoring a characteristic of the patient's breathing pattern, predicting a high breath state if a change in characteristic over a period of time is a positive value and exceeds a predetermined threshold, then a low breath state is predicted if the change in characteristic over a period of time is a negative value that has an absolute value that exceeds the predetermined limit; and apply appropriate treatment to the patient based on the predicted state. Method according to claim 17, characterized in that the characteristic is peak flow, or tidal volume. Method according to claim 17, characterized in that the period of time is dependent on various breathing cycles. A method of releasing pressurized breath gas to a patient's airway, characterized by the fact that it comprises: Releasing a flow of gas to the patient's airway from a source of respiratory gas via a patient circuit; a characteristic of the patient's breathing pattern, determining a higher threshold value of the characteristic based on the patient's breathing pattern, determining a lower threshold value of the characteristic based on the patient's breathing pattern; increase the fraction of inspired carbon dioxide if the value of the characteristic exceeds the upper threshold. 21. A method for determining an optimal therapeutic window in the treatment of a patient, which comprises: applying a dose of appropriate treatment to the patient based on a predicted or existing state of respiration; patient instability in response to the applied dose, record a series of data points representing instability indices for each of a series of responses; and adjust a therapeutic window corresponding to the dose applied with the instability index below the data points for which the measured instability index exceeds an acceptable value and above the data points for which the measured instability index is below an acceptable value. Method according to claim 21, characterized in that the instability index is: (a) a minimum and maximum peak flow ratio, (b) a minimum and maximum tidal volume ratio, (c) a slope of a line adjusted to a medium or median peak flow of the moving line, (d) a slope of a line adjusted to a medium or median tidal volume of the moving line, or (e) a measure or handle gain predictor of the patient's respiratory control system. 23. Method for treating a patient within an ideal therapeutic window, characterized by the fact that it comprises: applying a dose of appropriate treatment to the patient based on a predicted or existing state of respiration, measuring a patient instability index. in response to the dose applied; record a series of data points representing the instability indices for each of a response series; adjust a therapeutic window that corresponds to the dose applied with the instability index below the data points for which the index measured instability exceeds an acceptable value and above data points for which the measured instability index is below an acceptable value; and subsequent doses of treatment within the therapeutic window. A method according to claim 23, characterized in that the instability index is: (a) a ratio of minimum and maximum peak flow, (b) a ratio of minimum and maximum tidal volume, (c) a slope of a line adjusted to a median or median peak of the movement window, (d) a slope of a line adjusted to a median or median tidal volume of the movement window, or (e) a gain measure or predictor of the patient's respiratory control system.